this one works for me.

<?xml version="1.0" encoding="UTF-8"?>
<xp:view xmlns:xp="http://www.ibm.com/xsp/core"
    dojoParseOnLoad="true">
    <xp:this.resources>
        <xp:dojoModule name="dijit.layout.ContentPane"></xp:dojoModule>
        <xp:dojoModule name="dijit.layout.SplitContainer"></xp:dojoModule>

        <xp:dojoModule name="dijit.layout.TabContainer"></xp:dojoModule>
    </xp:this.resources>

    <div id="mainTabContainer" dojoType="dijit.layout.TabContainer"
        style="width:400px;height:200px">
        <div id="tab1" dojoType="dijit.layout.ContentPane"
            title="First Tab" selected="true" closable="false">
            First Tab
        </div>
        <div id="tab2" dojoType="dijit.layout.ContentPane"
            title="Second Tab" closable="true">
            Second Tab
        </div>
        <div id="tab3" dojoType="dijit.layout.ContentPane"
            title="Third Tab" closable="true">
            Third Tab
        </div>
    </div>
    <xp:button value="Label" id="button1">
        <xp:eventHandler event="onclick" submit="false">
            <xp:this.script><![CDATA[ var TabContainer = dijit.byId("mainTabContainer");

var subTab = dijit.byId("tab1");
TabContainer.selectChild(subTab);]]></xp:this.script>
        </xp:eventHandler></xp:button></xp:view>

I had simply dragged the DOJO controls onto the xPage as they are simply there in V9.0.. A glance at the source browser source code revealed that their ID tags get significantly modified for the client side.

I needed to change 

var TabContainer = dijit.byId("djTabContainer1");  

to

TabContainer = dijit.byId("view:_id1:djTabContainer1");

and

var subTab = dijit.byId("djTab_map");

to

var subTab = dijit.byId("view:_id1:djTabContainer1:djTab_map");

TBear